Field of the Invention
The present invention relates to an electrical element comprising a layer of a polymeric material having an electrical conductivity gradient based on conductive carbon fillers, which layer is intended to improve resistance to breakdown and resistance to ageing in a damp environment under electrical voltage.
The present invention typically, but not exclusively, applies to the field of medium-voltage power cables (voltages especially ranging from 6 to 45-60 kV) or high-voltage power cables (voltages especially higher than 60 kV and possibly ranging as high as 500-600 kV and even up to 800 kV) whether they are DC or AC power cables.
It may be used as a polymeric layer encircling the electrical conductor of this type of cable; or even as a polymeric layer in a fitting used with this type of cable, such as, for example, a terminal or a joint.
More particularly, the layer according to the invention is intended to be positioned at the interface between a conductive material (e.g. an electrical conductor, semiconductive layer, etc.) and an electrically insulating material (e.g. an electrically insulating layer).
Description of Related Art
The discontinuity in the electrical properties between an electrically insulating material and a conductive (or semiconductive) material may lead to local concentration of the electric field via the accumulation of space charges or charged species that are liable to initiate treeing under the action of an electric field.
In particular, the presence of moisture combined with the presence of an electric field with a polymeric material promotes gradual degradation of the insulating properties of medium- and high-voltage power cables.
This degradation mechanism, well known in the art as “water treeing”, may thus lead to breakdown of the electrical cable in question, and is therefore a considerable threat to the reliability of a power distribution network with well-known economic consequences due to short-circuits.